Papers by Ernst-michael Ilgenfritz
Nuclear Physics B, Aug 25, 1974
Inclusive two-particle correlations in rapidity variables between π+ π−, π+ π+ and π− π− obtained... more Inclusive two-particle correlations in rapidity variables between π+ π−, π+ π+ and π− π− obtained in 40 GeV π− p collisions are discussed in the framework of the Mueller Regge model and the multiperipheral cluster model. The data show features similar to the data reported at much higher energies from the CERN ISR. This behaviour is more easily understood from the multiperipheral cluster model. Data on transverse momentum correlations in the same reactions can be qualitatively understood from the same model.
We discuss Monte Carlo results relevant to the deconfinement order parameter and its fluctuation ... more We discuss Monte Carlo results relevant to the deconfinement order parameter and its fluctuation from the viewpoint of the dilute instanton gas approximation. We find a threshold effect in the Wilson string distribution due to instanton effects. On the basis of these data we determine a relation between the saturation temperature of the instanton gas and the confinement temperature. We also present other results of the numerical calculation.
The finite-temperature phase structure of lattice QCD with twisted-mass Wilson fermions
We study the properties of Nambu monopoles and Z-vortices in the 3D lattice SU(2) Higgs theory wh... more We study the properties of Nambu monopoles and Z-vortices in the 3D lattice SU(2) Higgs theory which represents the Standard Model at high temperature. We show that the densities of the Nambu monopoles and the Z-vortices are O(1) in the symmetric phase and generically small in the Higgs phase. Near to the critical Higgs mass and in the vicinity of the phase transition the densities are no more negligible in the broken phase. The percolation probability of the Z-vortex lines is found as a new disorder parameter for this phase transition. We conclude that the transition to the symmetric phase is accompanied by Z-vortex condensation. Simulations comparing elementary and extended vortices and monopoles at different β G values, aiming to show that the density of vortices and monopoles of fixed physical size might have a well-defined continuum limit, gives encouraging but so far inconclusive results.
Proceedings of The XXV International Symposium on Lattice Field Theory — PoS(LATTICE 2007)
We present selected recent results of the QCDSF collaboration on the localization and dimensional... more We present selected recent results of the QCDSF collaboration on the localization and dimensionality of low overlap eigenmodes and of the topological density in the quenched SU(3) vacuum. We discuss the correlations between the topological structure revealed by overlap fermions without filtering and the confining monopole and P-vortex structure obtained in the Indirect Maximal Center Gauge.
Proceedings of XXIIIrd International Symposium on Lattice Field Theory — PoS(LAT2005)
Proceedings of XXIIIrd International Symposium on Lattice Field Theory — PoS(LAT2005)
Overlap fermions, which preserve exact chiral symmetry on the lattice, provide a powerful tool fo... more Overlap fermions, which preserve exact chiral symmetry on the lattice, provide a powerful tool for investigating the topological structure of the vacuum. Applying this formulation to zerotemperature quenched SU(3) configurations generated by means of the Lüscher-Weisz action, we define the topological charge density with and without UV filtering and study its properties by looking at the density profile and the two-point correlation function. We observe that the density possesses global sign coherent structures, which get increasingly tangled as more and more modes are included. This change of the structure is also detected by the increasing negative tail of the two-point function. We also study the inverse participation ratio of the eigenmodes and discuss their dimensionality.
Proceedings of Xth Quark Confinement and the Hadron Spectrum — PoS(Confinement X)
Proceedings of Light Cone 2010: Relativistic Hadronic and Particle Physics — PoS(LC2010)
We calculate the gluon structure function of a color dipole in a new approach evaluating the matr... more We calculate the gluon structure function of a color dipole in a new approach evaluating the matrix elements of SU(2) gluon field operators separated along a direction close to the light cone. As vacuum state in the pure glue sector, we use a variational ground state of the near-light-cone Hamiltonian. With a mean momentum fraction of the gluons fixed to the "experimental value" in a proton, the resulting gluon structure function for a dipole state with four links is compared qualitatively to the NLO MRST 2002 parameterization at Q 2 = 1.5 GeV 2 .
Proceedings of The XXVII International Symposium on Lattice Field Theory — PoS(LAT2009)
Proceedings of VIIIth Conference Quark Confinement and the Hadron Spectrum — PoS(ConfinementVIII)
Proceedings of The 30th International Symposium on Lattice Field Theory — PoS(Lattice 2012)
We report about the current status of our ongoing study of the chiral limit of two-flavor QCD at ... more We report about the current status of our ongoing study of the chiral limit of two-flavor QCD at finite temperature with twisted mass quarks. We estimate the pseudo-critical temperature T c for three values of the pion mass in the range of m PS ≃ 300 and 500 MeV and discuss different chiral scenarios. Furthermore, we present first preliminary results for the trace anomaly, pressure and energy density. We have studied several discretizations of Euclidean time up to N τ = 12 in order to assess the continuum limit of the trace anomaly. From its interpolation we evaluate the pressure and energy density employing the integral method. Here, we have focussed on two pion masses with m PS ≃ 400 and 700 MeV.
Proceedings of The XXVIII International Symposium on Lattice Field Theory — PoS(Lattice 2010)
Proceedings of The XXVIII International Symposium on Lattice Field Theory — PoS(Lattice 2010)
We calculate perturbative Wilson loops of various sizes up to loop order n = 20 at different latt... more We calculate perturbative Wilson loops of various sizes up to loop order n = 20 at different lattice sizes for pure plaquette and tree-level improved Symanzik gauge theories using the technique of Numerical Stochastic Perturbation Theory. This allows us to investigate the behavior of the perturbative series at high orders. We observe differences in the behavior of perturbative coefficients as a function of the loop order. Up to n = 20 we do not see evidence for the often assumed factorial growth of the coefficients. Based on the observed behavior we sum this series in a model with hypergeometric functions. Alternatively we estimate the series in boosted perturbation theory. Subtracting the estimated perturbative series for the average plaquette from the non-perturbative Monte Carlo result we estimate the gluon condensate.
Proceedings of The XXVII International Symposium on Lattice Field Theory — PoS(LAT2009)
We complete our high-accuracy studies of the lattice ghost propagator in Landau gauge in Numerica... more We complete our high-accuracy studies of the lattice ghost propagator in Landau gauge in Numerical Stochastic Perturbation Theory up to three loops. We present a systematic strategy which allows to extract with sufficient precision the non-logarithmic parts of logarithmically divergent quantities as a function of the propagator momentum squared in the infinite-volume and a → 0 limits. We find accurate coincidence with the one-loop result for the ghost self-energy known from standard Lattice Perturbation Theory and improve our previous estimate for the two-loop constant contribution to the ghost self-energy in Landau gauge. Our results for the perturbative ghost propagator are compared with Monte Carlo measurements of the ghost propagator performed by the Berlin Humboldt university group which has used the exponential relation between potentials and gauge links.
Proceedings of The XXVII International Symposium on Lattice Field Theory — PoS(LAT2009)
We calculate Wilson loops of various sizes up to loop order n = 20 for lattice sizes of L 4 (L = ... more We calculate Wilson loops of various sizes up to loop order n = 20 for lattice sizes of L 4 (L = 4, 6, 8, 12) using the technique of Numerical Stochastic Perturbation Theory in quenched QCD. This allows to investigate the behaviour of the perturbative series at high orders. We discuss three models to estimate the perturbative series: a renormalon inspired fit, a heuristic fit based on an assumed power-law singularity and boosted perturbation theory. We have found differences in the behavior of the perturbative series for smaller and larger Wilson loops at moderate n. A factorial growth of the coefficients could not be confirmed up to n = 20. From Monte Carlo measured plaquette data and our perturbative result we estimate a value of the gluon condensate α π GG .
Proceedings of The XXVII International Symposium on Lattice Field Theory — PoS(LAT2009)
Lattice results for the gluon propagator in SU(2) pure gauge theory obtained on large lattices ar... more Lattice results for the gluon propagator in SU(2) pure gauge theory obtained on large lattices are presented. Simulated annealing is used throughout to fix the Landau gauge. We concentrate on checks for Gribov copy effects and for scaling properties. Our findings are similar to the ones in the SU(3) case, supporting the decoupling-type infrared behaviour of the gluon propagator.
Proceedings of The XXV International Symposium on Lattice Field Theory — PoS(LATTICE 2007)
We present recent results on the Landau gauge gluon and ghost propagators in SU(3) pure gauge the... more We present recent results on the Landau gauge gluon and ghost propagators in SU(3) pure gauge theory at Wilson β = 5.7 for lattice sizes up to 80 4 corresponding to physical volumes up to (13.2 fm) 4. In particular, we focus on finite-volume and Gribov-copy effects. We employ a gauge-fixing method that combines a simulated annealing algorithm with finalizing overrelaxation. We find the gluon propagator for the largest volumes to become flat at q 2 ∼ 0.01 GeV 2. Although not excluded by our data, there is still no clear indication of a gluon propagator tending towards zero in the zero-momentum limit. New data for the ghost propagator are reported, too.
Proceedings of XXIVth International Symposium on Lattice Field Theory — PoS(LAT2006)
We summarize the current status of our numerical results for the gluon and ghost propagators and ... more We summarize the current status of our numerical results for the gluon and ghost propagators and for the Kugo-Ojima confinement parameter in quenched SU(3) lattice Landau gauge theory. The data for the propagators are compared to our results obtained in the case of full QCD, simulated using two flavors of dynamical clover-improved Wilson fermions. We demonstrate that the infrared behavior of the ghost propagator is consistent with the Kugo-Ojima confinement criterion. Explicit violation of reflection positivity by the gluon propagator is shown. Additionally, we present results of a running coupling constant both at low and at large momenta.
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Papers by Ernst-michael Ilgenfritz